Although recent studies have revealed a great deal about the molecular basis of drug addiction, numerous gaps remain in our understanding of the changes in gene expression that are associated with chronic drug intake. One prominent alteration that occurs upon chronic cocaine exposure is accumulation in the striatum of very stable isoforms of the transcription factor d FosB that is produced by alternative splicing of the FosB transcript. The delta FosB isoforms may mediate some of the neural and behavioral modifications that occur with drug addiction. The factors that play a role in the alternative splicing of delta FosB have not yet been identified. To begin to understand the posttranscriptional events that lead to the production of stable dFosB we will test the hypothesis that both cis- and trans-acting factors are important in this regulation. Mutation analysis of FosB will be used to identify the sequences essential for pre-mRNA splicing. Cross-linking and RNA-binding studies will be undertaken to determine which trans-acting factors bind to the RNA regulatory sequences in splicing extracts prepared from tissue culture cells and brains. Factors identified in these studies will be tested in splicing assays to determine if they regulate splicing in vitro. The distribution of the regulatory splicing factors within the brain will be determined using in situ hybridization histochemistry. The expression of the regulatory factors will be changed in order to determine the effect on FosB in vivo. These studies will identify the factors required for the regulation of splicing during chronic cocaine use and lead to an understanding of the mechanisms involved. Because dFosB is also induced by chronic administration of other drugs of abuse, such as amphetamine, nicotine and opiates, the results obtained in this study may also lead to a better understanding of drug addiction.